1. Field of the Invention
The present invention relates to stable non-aqueous slurries of water soluble polymers. More specifically, the slurries are characterized by having as their medium low molecular weight polyethylene glycol, and as a stabilizer, an amine phosphate ester salt.
2. Technology Description
Hydrophilic polymers or gums are widely used in industry. They are used to thicken, suspend or stabilize aqueous systems. These gums can produce gels or act as emulsion stabilizers, flocculants, binders, film formers, lubricants and friction reducers. In each of these applications, the polymers are used to adjust and control the rheological properties of the aqueous system to which they are being added.
For commercial and industrial applications, rapid addition of these gums to water is highly desirable. Doing so, however, often results in the formation of lumps of unhydrated polymer. These lumps are gel-like substances, wet on the outside but dry on the inside, that form as a result of the polymer beginning to hydrate before the polymer molecules are dispersed. Once the outer layer of polymer is hydrated, the lump or fisheye often cannot be dispersed even with vigorous mixing. Removal of these lumps results in significant losses of time, material and polymer efficiency.
These lumps are particularly problematic in the oil and gas industry where water soluble polymers are used downhole during drilling, workover, completion, stimulation and reservoir flooding operations. These unhydrated lumps, inert to enzymes, chemical breakers and acids, cause a variety of problems including plugging of the well and permeability impairment of the oil bearing strata. In addition, when polymers are used they are typically added to water in a dilute solution. During
this operation fugitive dust is often generated. This dust has a number of potential detrimental effects. The dust can be inhaled by workers preparing the solution. Some of the polymers which can be suspended in a non-toxic solvent produce dust when handled in a powdered form which may produce a respiratory allergenic response and/or irritation to some individuals. Dust can also drift to areas where it is not intended.
To avoid lump or dust formation and its associated problems, the polymers can be added to the aqueous systems as liquid slurries. A number of methods for accomplishing this, and the compositions prepared thereby, are described in the prior art. Unlike the present invention, they often use oil carriers (e.g., mineral or diesel) to suspend and deliver the polymers to the aqueous systems. In addition to the oil carrier fluid, these slurries usually contain clay or clay like particulates which act to viscosity and stabilize the non-aqueous suspension. The disadvantages of these carrier systems is that attempts to eliminate the oil, often an undesirable component, result in the substitution of oil by toxic glycol ether. The clay component itself is also often times an undesirable component. This is particularly true in oil and gas field applications where incorporation of the clay into the slurries, which is necessary to keep the polymer in solution, impairs the permeability of the oil or gas bearing strata. This is the very problem caused by the formation of fisheyes that the oil slurry is supposed to eliminate.
U.S. Pat. No. 4,176,107 discloses liquid polymer compositions and to methods of preparing these compositions which comprise a high molecular weight water-soluble vinyl addition polymer, water, one or more surfactants, and a water-soluble polyalkylene glycol, or water-soluble ethoxylated alcohol, alkylphenol or fatty acid. U.S. Pat. No. 4,453,979 describes the use of water with a high molecular weight blend of water and polyethylene glycol to disperse hydrophilic gums. European Publication 58 017 describes the use of a water and clay based drilling fluid which contains high molecular weight PEG. PEG ranging in molecular weight from 1000 to 10,000,000, which are solid at room temperature, are mentioned. U.S. Pat. No. 4,799,962 discloses a particulate water-soluble polymer is dispersed in a liquid medium comprised of low molecular weight polyethylene glycol, water and high molecular weight polyethylene glycol in amounts sufficient to impart stability to the dispersion. U.S. Pat. No. 5,362,312 discloses a carrier for water-soluble polymers which includes polyethylene glycol; one or more viscosified polyol fluid components; and one or more viscosifying polysaccharides.
Despite the above teachings, there still exists a need in the art for liquid slurries for water-soluble polymers which are environmentally friendly, are extremely stable over long periods of time and are operative over a wide temperature range.